In the design and manufacture of a three-dimensional article, it is common practice to first create an initial design and then manually produce a custom prototype, or model, of the article based upon the initial design. After reviewing the initial prototype, design revisions are often made requiring the production of yet another prototype. This process of review and redesign may be repeated a number of times before finding the desired design thereby requiring a number of iterative steps to produce a single finished article. Accordingly, the process of designing and prototyping an article may involve considerable time, effort and expense.
Computer aided design (CAD) is commonly used for automating the design process. With the aid of a suitable computer, an operator is able to design a three-dimensional article and display the design on a two-dimensional medium, such as a display screen or paper. A significant advance in the art of three-dimensional design and modeling is disclosed in U.S. Pat. No. 4,665,492 to Masters entitled "Computer Automated Manufacturing Process and System." This patent discloses an apparatus including a positionable ejection head for ballistically emitting small mass particles to construct a three-dimensional article based upon article defining data. In other words, the patent discloses the advantageous combination of CAD with an apparatus for precisely constructing the article based upon the generated CAD data.
Another method and apparatus for forming three-dimensional objects is disclosed in U.S. Pat. No. 5,136,515 to Helinski entitled "Method and Means for Constructing Three-Dimensional Articles by Particle Deposition." This patent discloses a device including two positionable jetting heads with two feeder lines connected to respective remote sources of melted wax, for example, to provide both object and support material.
The formation of three-dimensional articles by jetting a photosetting or thermosetting material is disclosed in U.S. Pat. No. 5,059,266 to Yamane et al. entitled "Apparatus and Method for Forming Three-Dimensional Article." A jet sequentially or intermittently jets the photosetting or thermosetting material in a droplet form along a flight path to a stage on which the article is constructed.
A conventional jet or jetting head may require a constant, uninterrupted, supply of liquid build material delivered thereto. If the supply is interrupted, the processor or controller may still continue to position and attempt to fire the jet. However, a portion of the article may fail to be formed if the flow of material is interrupted.
U.S. Pat. No. 5,260,009 to Penn entitled "System, Method, and Process for Making Three-Dimensional Objects" discloses yet another apparatus for forming three-dimensional articles wherein a second or support material is dispensed with each layer of the three-dimensional article as it is formed, and wherein feeder lines provide a source of the liquid material to a plurality of jets carried by a movable head. An inspection station is provided for the jets and includes a conveyor belt which received drops of melted media from the jets. An optical sensor scans the parallel lines produced by simultaneous operation of the jets. If a jet is malfunctioning, the jets are directed to complete a purge-and-wipe for expulsion of any foreign matter. Proper operation of the jets is determined before beginning formation of an article; thus, errors occurring during construction of an article would go undetected. In addition, wiping of the jets may unfortunately serve to introduce foreign matter into the relatively small jet orifices, thereby plugging the orifices.
U.S. Pat. No. 5,303,141 to Batchelder et al. entitled "Model Generation System Having Closed-Loop Extrusion Nozzle Positioning" discloses an apparatus including an extrusion head for extruding a bead of material, such as a hot melt adhesive. A feedback sensor is provided to permit the extruder to adjust to a number of different mechanisms. For example, when the extruded bead is applied around a convex or concave contour the bead, while it is still hot enough to be pliable, the bead tends to distort to minimize its length. Also, and dependent on the distance from the nozzle to the underlying material, the extruded bead may change its deposited cross-section as a function of this distance. Also, back pressure from already deposited material that is near the nozzle may reduce the flow rate out of the nozzle, and changes in temperature or composition of the material to be extruded may change the rate at which the material flows out of the nozzle and, as a result, the rate at which the material solidifies to its final dimension. The patent discloses that the feedback provided by the sensor is important to permit the extruder to adjust to a number of different mechanisms which may operate to cause only the extruded material to have dimensions other than those intended. However, many other factors may affect accuracy, and the speed of construction of the intended article. In addition, the patent discloses that the deposition feedback sensor functions to provide information regarding only the most recently extruded material. Accordingly, errors which occur subsequently in the article may go undetected.